Add failing test case. Nesting the same mixin in content blocks more than once fails with an invalid loop detection error.
Add failing test case. Nesting the same mixin in content blocks more than once fails with an invalid loop detection error.

PMArtz92/sass,modulexcite/sass,Galactix/sass,dylannnn/sass,danielfein/sass,modulexcite/sass,nicklima/sass,jaroot32/sass,PMArtz92/sass,HugoRLopes/sass,nickg33/sass,antonifs/sass,MetaAshley/sass,14113/sass,Iamronan/sass,hcatlin/sass,jaroot32/sass,OrenBochman/sass,liquidmetal/sass,lmetla/sass,JuanitoFatas/sass,HugoRLopes/sass,srawlins/sass,zaru/sass,tenderlove/sass,Ahnita/sass,stewx/sass,saper/sass,Andrey-Pavlov/sass,tangposmarvin/sass,schneems/sass,schneems/sass,antonifs/sass,JuanitoFatas/sass,baiyanghese/sass,oss-practice/sass,saper/sass,StephanieMak/sass,cmpereirasi/sass,lmetla/sass,briangonzalez/sass,ridixcr/sass,dylannnn/sass,chriseppstein/sass,srinivashappy/sass,rammy7219/sass,srawlins/sass,Ahnita/sass,Nzaga/sass,nicklima/sass,Industrys/sass,amitsuroliya/sass,Industrys/sass,nickg33/sass,liquidmetal/sass,zaru/sass,cmpereirasi/sass,rammy7219/sass,DanteKaris/sass,OrenBochman/sass,tangposmarvin/sass,DanteKaris/sass,xzyfer/sass,hcatlin/sass,Andrey-Pavlov/sass,Iamronan/sass,amitsuroliya/sass,Anshdesire/sass,Galactix/sass,srinivashappy/sass,MetaAshley/sass,ridixcr/sass,danielfein/sass,askl56/sass,Nzaga/sass,xzyfer/sass,Anshdesire/sass,stewx/sass,askl56/sass,StephanieMak/sass